there are a variety of programs made by people who use aim such as "aim invader", which use multiple screen names created by the user to spam people with various types of requests that aim accepts, such as file transfer and chat room invitation, there are several others, in any case, if one user is bombarded with enough of these requests it will freeze AIM, the best defense is change your aim preferences so that everything must go through a dialogue box for you to accept, or just block it completly if you know that you don't use that feature, and also chance your buddy list preferences to only allow people on your buddy list to contact you as FatPhantom said in an earlier post, short of not using AIM alltogether, that is the only advice i can offer.

cheers

edit : sorry i didn't see that memory had posted the same thing as i did, he got to it before i did , sorry about that.